Comparative analysis of Shigella and Campylobacter transmission in paired longitudinal household cohort studies in urban Bangladesh and rural Tanzania
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Background
Transmission pathways of enteric pathogens have been broadly characterized; however, the degree to which different pathogens exploit different transmission routes and how these patterns vary across age remain poorly understood. We quantified the relative contribution of within-household (infection sources internal to the household) and community-to-household (infection sources external to the household) transmission for Shigella and Campylobacter .
Methods
We conducted paired longitudinal cohort studies in urban Bangladesh and rural Tanzania, each enrolling 100 households with a child under the age of one year. Stool samples were collected from participants’ households monthly and during diarrheal episodes for one year. We estimated daily infection trajectories for each participant for Shigella and Campylobacter . We used these data in a household transmission model, estimating within-household and community-to-household transmission rates by pathogen, age group, and study site, using forward selection to identify interactions.
Findings
Overall, 8.8% of Campylobacter and 7.6% of Shigella infections were symptomatic. The incidence of Shigella and Campylobacter was 2.3 and 1.4 times higher, respectively, in Bangladesh compared to Tanzania. Crude associations suggest that Campylobacter had greater community-to-household versus within-household transmission compared to Shigella , but these patterns were better explained by interactions with age. Specifically, children <5 years had higher transmission rates for Campylobacter than Shigella , and, for both pathogens, higher community-to-household than within-household transmission rates. Those ≥5 years had higher Shigella transmission.
Interpretation
Apparent pathogen-specific differences in transmission patterns for Shigella and Campylobacter were driven by effect modification by age. Intervention design should consider age-specific transmission patterns along with pathogen biology.
Funding
The research was supported by R01 AI153254 and R01 TW012183 from the National Institutes of Health.
Conflict of interest
Research in context
Evidence before this study
Previous studies have identified person-to-person, environmental, and zoonotic transmission routes as important transmission pathways for enteric pathogens, but their relative contributions remain uncertain. On June 22, 2026, we searched PubMed using the following search terms: (“ Shigella ” OR “ Campylobacter ”) AND (“transmission route” OR “transmission path” OR “source attribution” OR “infection source”) AND (“household” OR “community” OR “environment” OR “food” OR “water” OR “person-to-person” OR “animal”) with no restrictions on language or publication date. We identified 153 records, of which 63 were considered after title and abstract screening. The vast majority of studies focused on infection source attribution for Campylobacter in high-income countries, emphasizing its strong environmental persistence and identifying community-acquired infections from contaminated food (typically poultry and cattle) as the primary sources of infection. By contrast, studies on Shigella transmission routes were limited, with most publications reporting results based on expert opinion, which typically concurred that transmission primarily occurs via person-to-person transmission and within households. The studies largely focused on biological properties of the pathogens and rarely examined how transmission patterns varied across age groups. Furthermore, no studies directly quantified or compared the relative contributions of specific transmission routes for both Shigella and Campylobacter .
Added value of this study
Using longitudinal household data from an urban setting (Dhaka, Bangladesh) and a rural setting (Haydom, Tanzania) combined with a mechanistic household transmission model, we quantified the relative contribution of within-household and community-to-household transmission for both Shigella and Campylobacter . In models not accounting for participant age, community-to-household transmission was more dominant for Campylobacter compared to Shigella . However, pathogen-specific differences in the relative contribution of community-to-household versus within-household did not persist after accounting for interactions between age and the other predictors. We identified substantial differences in transmission patterns across age groups, with community-to-household transmission consistently dominating among children <5.
Implications of all the available evidence
The literature on the transmission routes of enteric pathogens typically emphasizes pathogen biology, focusing on infectious dose or environmental persistence to understand likely transmission pathways. Known biological differences between Campylobacter and Shigella (e.g., that Campylobacter is more persistent in the environment and has a higher infectious dose than Shigella ) could influence the transmission routes each pathogen can exploit, leading to assumptions that Campylobacter transmission is inherently driven by external sources. However, our results suggest that population-level transmission patterns cannot be inferred from pathogen biology alone. The relative importance of transmission from household members versus other sources varies substantially by age, with particularly strong contributions from non-household sources among young children. Interventions to reduce enteric pathogen transmission should consider the age-specific transmission patterns of the target population in addition to the biological characteristics of the pathogen.
